Thanks Torrent, appreciate how valuable time gets with a 20 month baby in the background.
So might hope for roughly 12% extra distance with the 36v 12A Lead Acid over 24v 8A Li-on.
The extra weight would presumably loose a bit of that, but it's unlikely to be worst for the same distance.
Tempted, as the lead & steel is 60% of the alloy frame / li-on & it would make an interesting comparison between the 2 bikes.